This invention relates to a water-cooled welding gun and particularly to a novel method for cooling the gas shielding nozzle.
This invention is particularly useful on those electric arc welding torches of the type wherein a consumable electrode is directed toward a workpiece through an inner or guide tube, and where the electric arc is protected by shielding gas directed toward the arc by a nozzle.
A typical torch includes an elongated inner tube having a central opening which carries the consumable electrode and shielding gas and a contact tip at the end. In high amperage environments, means are usually provided for cooling the contact tip, otherwise it will be damaged by overheating and melting. One common technique is to provide the tube with passageways surrounding the central opening through which cooling water is circulated. In addition to cooling the contact tip, the gas shielding nozzle should also be cooled, otherwise metal splattered from the weld will tend to adhere to it. It has been found that the hotter the nozzle, the more tenaciously the splatter will adhere to it.
The welding operator will frequently attempt to clean the nozzle, and by doing so will roughen its surface and as a consequence, the splatter will adhere even more tightly to it. Frequently, the welder will attempt to remove the splatter by striking the nozzle against a hard surface. Therefore, those nozzles that are not adequately cooled have a relatively short lifespan, not only because of the direct effects of over heating, but also because of physical abuse.
Prior art attempts to provide cooling for the nozzle have included the use of a thermally conductive but electrically insulative material, such as a ceramic sleeve placed between the nozzle and the water cooled tube, or by means of a material, such as aluminum oxide, which is first flame sprayed onto the outer surface water cooled tube, and then the nozzle secured thereto.
In those guns using a ceramic ring, the surface area between the nozzle and the water cooled member is limited, thus limiting the cooling efficiency of that arrangement. Flame sprayed Al.sub.2 O.sub.3 is difficult to apply to a high dimensional tolerance, and this material is too hard to be ground to size efficiently.